1. Field of the Invention
The present invention relates to an antifoulant dispersant. The present invention particularly relates to antifoulant dispersants for use with centrifugal compressors used for compression in an ethylene process.
2. Background of the Art
Fouling of compressors is a well-known problem in processes using them. The fouling of compressors can cause damage to the compressors as well as plant down time, both potentially very expensive problems. There has been considerable effort spent by industry to prevent such fouling. For example, U.S. Pat. No. 6,159,547 to McMordie, et al., discloses a method for coating turbomachinery having a metal surface to prevent fouling. The steps of the method are applying to the surface a first slurry containing an acidic aqueous medium containing a galvanically active material and phosphate ions, thereby forming a galvanically sacrificial first layer, curing the first layer, applying to the cured first layer an aqueous non-conductive second slurry containing inorganic phosphate or silicate ions, thereby forming a non-conductive second layer, curing the second layer, applying to the cured second layer a liquid sealer composition containing a thermally stable organic polymer and fluorocarbon, thereby forming a top layer, and curing the top layer.
In some processes, the operating conditions under which the compressors are laboring can foul or even erode compressor blades, no matter how well coated the compressor blades may be. For example, U.S. Pat. No. 5,849,983 to Khatib discloses addition of polyisobutylene to a predominantly gaseous stream for preventing the shearing of hydrocarbon droplets in the stream to aerosol sizes. One advantage of this invention is that when the polyisobutylene is sprayed upstream of compressor stations, it functions to prevent fouling and erosion of the compressor blades.
While a polymer can function to prevent fouling, as is disclosed in U.S. Pat. No. 5,849,983 to Khatib, in some processes, it is the formation of polymers that can cause fouling. For example, in an ethylene process, it is the formation of organic polymers that can cause compressor fouling.
Steam cracking of hydrocarbons accounts for virtually all of the ethylene produced worldwide. Hydrocarbons used as ethylene feedstocks range from natural gas liquids including ethane, propane and butane, to petroleum liquids including gas oils and naphtha. In the process of producing ethylene, as the ethylene is produced and purified, small amounts of polymers can form. These polymers are generally considered contaminants and are undesirable in the product ethylene. One point of isolation of such contaminants is the compressors. Due to pressure changes, the contaminants can be isolated as liquids and sent to knockout pots wherein the contaminants are held until sent for recycle or disposal.
In one aspect, the present invention is a dispersant prepared from a formulation comprising: (a) the reaction product of a polyalkyl polyamine, an alkylphenol and an aldehyde; and (b) a polyalkyl acrylate polymer; wherein the two components are present in a weight ratio of about 2:1.
In another aspect, the present invention is a process for preventing fouling of compressor blades used to compress gasses comprising depositing a dispersant onto blades of a compressor to be protected from fouling, the dispersant being prepared from a formulation comprising: (a) the reaction product a polyalkyl polyamine, an alkylphenol and an aldehyde; and (b) a polyalkyl acrylate polymer; wherein the two components are present in a weight ratio of about 2:1.
It would be desirable in the art of compressing gasses to prevent fouling of compressor blades. It would be particularly desirable in the art of compressing ethylene to prevent fouling of compressor blades while avoiding creating an emulsion in knockout pots.
In one aspect, the present invention is a process for preventing fouling of compressor blades used to compress gasses. The dispersants of the present invention function to prevent fouling in compressors by forming a film on the surface of the compressor blades that prevents, or at least mitigates, buildup by polymers and other contaminants in the gasses being compressed.
In the practice of the process of the present invention, the dispersants can be applied to compressor blades in any way known to those of ordinary skill in the art of applying such materials to be useful for preventing fouling. Preferably, the dispersants are sprayed onto the compressor blades in the form of an aerosol. More preferably, the dispersants are injected into the gas stream being compressed, upstream of the compressor, as an aerosol that is then carried to the compressor blades by the gas being compressed.
In another aspect, the present invention is a dispersant prepared from a formulation having at least two components. The first component of the dispersant, hereinafter Component A, is the reaction product of a polyalkyl polyamine, an alkylphenol and an aldehyde. The polyalkyl polyamines useful with the present invention have a general formula: 
wherein n is an integer of from 0 to 5. Exemplary amines include, but are not limited to ethylene diamines and tetraethylenepentamine, but any compound having the general formula I can be used to prepare Component A of the present invention.
The alkylphenols useful to prepare the Component A of the present invention have the general formula: 
wherein R is an alkyl group having from 1 to 120 carbons. Exemplary alkylphenols that can be used to prepare Component A of the present invention include but are not limited to anisole, polybutylphenol and nonylphenol, but any alkylphenol having the above general formula can be used.
The aldehydes useful for preparing the first component of the present invention have the general formula: 
wherein R is H or an alkyl group having from 1 to 6 carbons. Preferably the aldehyde is formaldehyde.
Component A is the reaction product of a polyalkyl polyamine, an alkylphenol and an aldehyde. Component A is preferable a Mannich condensation product formed by condensing the alkylphenol of Formula II with an aldehyde of Formula III and a polyalkyl polyamine of Formula I. The condensation reaction may be conducted at a temperature in the range of about 40xc2x0 C. to about 200xc2x0 C. The reaction can be conducted in bulk (no diluent or solvent) or in a solvent or diluent. Water is evolved and can be removed by azeotropic distillation during the course of the reaction. The aldehyde is typically present in a molar amount at least equal to the total molar amount of the amine compounds present. Component A can be prepared by any method known to those of ordinary skill in the art of preparing such reaction products to be useful.
Any ratio of alkylphenol to aldehyde to polyalkyl polyamine that will form a stable reaction product can be used to prepare Component A of the present invention. Preferably, the weight ratio of alkylphenol to aldehyde is from 0.1:1 to 60:1. Preferably the weight ratio of aldehyde to polyalkyl polyamine is from 1:1 to 6:1.
The second component of the dispersant of the present invention is a polyalkyl acrylate polymer. For the purposes of the present invention, the term xe2x80x9cacrylate polymersxe2x80x9d include polymers having repeating acrylate units, methacrylate units and mixtures thereof. The polymer is preferably a copolymer. These copolymers are typically prepared by first preparing an ester of acrylic acid or methacrylic acid and a C1-C10 alcohol and then reacting the ester with a N-vinyl pyrrolidinone or vinylpyridine. For example, VISCOPLEX(copyright) 6-917, available from RohMax, is a polyalkyl methacrylate copolymer which can be used as Component B of the present invention.
While copolymers are a preferred embodiment, polyalkyl acrylate polymers are also useful as component B. For example, poly (isodecyl methacrylate) can be used as component B of the present invention. Other polymers having utility as Component B of the present invention include poly (tert-butyl methacrylate), poly (nonyl acrylate), poly (cyclohexyl methacrylate), poly (butyl acrylate) and poly (octadecyl methacrylate).
The polyalkyl acrylate polymers and copolymers useful for preparing component B of the present invention are present in the dispersant compositions of the present invention at a ratio of Component A:Component B of about 2:1. This ratio relates to xe2x80x9cactive polymerxe2x80x9d or polymer weight, not solution weight. For example, the VISCOPLEX 6-917 used in the examples is a solution of 41 percent polymer dissolved in a hydrocarbon solvent. Thus a ratio of Component A:Component B of 10:10 as set fourth in Example 1 is actually an active polymer ratio of 10:4.1 or 2:0.82. For purposes of the present invention, the ratio of Component A:Component B shall be about 2:1 when the weight of each material excluding solvents is present at a ratio of Component A to Component B of from 2:0.5 to 2:1.5. The ranges of from 2:0.8 to 2:1.2 and from 2:0.9 to 2:1.1 are also included within the range of about 2:1.
While the two-component embodiment of the dispersant of the present invention is effective at preventing the undesirable accumulation of polymers on compressor blades, there is a second embodiment of the dispersant of the present invention that also has the desirable property of not creating emulsions with resultant foaming in knockout pots. While this embodiment may not act to break existing emulsions, it does not itself cause emulsions, unlike many other dispersants used for preventing the undesirable accumulation of polymers on compressor blades.
In this second embodiment, the ratio of Component A to Component B remains at about 2:1, but Component A is itself two separate components present in approximately equal weight amounts, Component A1 and component A2. Component A1 is characterized as being a composition that is the reaction product of a polyalkyl polyamine, an alkyl phenol and an aldehyde prepared using a comparatively high molecular weight alkylphenol. For example, Component A1 could be prepared with a compound according to Formula II wherein R is an alkyl group having about 106 carbons. A polybutylphenol wherein the polybutylphenol has 26 repeating butylene units could be used to prepare such a Component A1. The weight ratio of phenol to formaldehyde to amine of such an A1 component can be 60:1:3 while the molar ratio of phenol to formaldehyde to amine can be 2:2:1
Component A2 is characterized as being a composition that it the reaction product of a polyalkyl polyamine, an alkyl phenol and an aldehyde prepared using a comparatively low molecular weight alkylphenol. For example, Component A2 could be prepared with a compound according to Formula II wherein R is an alkyl group having about 9 carbons. A nonylphenol could be used to prepare such a Component A2. For this A2 component, the weight ratio of phenol to formaldehyde to amine can be 3.7:1:1 while the molar ratio of phenol to formaldehyde to amine can be 1:2:1
The dispersants of the present invention are preferably used as a solution in a hydrocarbon. For example, the dispersants of the present invention can be admixed with kerosene, a heavy aromatic solvent, xylene, and the like prior to use to reduce viscosity and ease delivery of the dispersant onto compressor blades. While the solution can be at any concentration, preferably the composition is prepared and used as a from about 70 to about 90 percent, more preferably about 75 to about 85 percent, and most preferably an 80 percent solution of dispersant in solvent.